Food-related allergies are of clinical importance. Their
diagnostics covers a significant part of allergology clinic's work.
Allergic reactions to egg proteins are frequently diagnosed among
children but remain uncommon among adult patients. We report on
two cases of adult patients presenting with allergies to egg proteins,
ovalbumin and ovomucoid. In case of ovalbumin allergy, hen`s eggs
and quail egg`s are a source of the thermolabile antigen. In contrast,
ovomucoid is heat-resistant. Molecular allergy diagnostics support
the risk management of patients with suspected egg allergy.

Food allergies are reported by our patients with increasing
frequency. Diagnostics and care for food allergic patients
reperesent a significant percentage of workload in the allergy
clinic. Here, we will focus on egg-related allergies.

Hen eggs (Domus domesticus) are an important protein
source for human nutrition. Eggs and egg components are part of
various foods like mayonnaise, pasta, pastries, sausages, glazes,
salads, convenience food, and confectionary.

Egg allergies are predominantly seen during the first years
of live. Up to 2% of children and adolescents are affected [1-4].
Hen's eggs and cow milk are the most important food allergens
in childhood [2, 3]. Due to tolerance induction with increasing
age, the percentage of hen's egg allergies declines among adults
to only 12% of all food allergies [2-4].

Clinical symptoms can vary by severity and organs affected.
Symptomatology includes gastro-intestinal complaints,
dyspnoea, cutaneous reactions, and anaphylactic shock. The
severity of an allergic reaction depends upon sensitization,
allergen amount, and type of exposure [4]. The variability of
clincial signs and symptoms is a challenge for the allergologist to
advise patients in risk management.

In recent years, molecular diagnostics in allergology have
become reality. By detailed knowledge of relevant allergens
in complex allergen sources such as food, a tailored risk
management is facilitated.
The major known allergens of hen's eggs are ovalbumin,
conalbumin, ovomucoid, and lysozyme [1-4].
With the following case reports we want to illustrate modern
risk management in food allergies.

In consequence of this event she avoided quail eggs, the only
new food component. Hen's eggs were consumed by the patient
only hard boiled, what was well tolerated.

After detailed medical history, we performed prick tests with
the foods. The prick test for native hen's egg was positive (Fig.
1). Laboratory investigations demonstrated specific IgE against
ovalbumin 0.88 kUA/l (CAP-class 2), but not against any other
egg component.

Limitations: Double-blinded oral provocation is used for
confirmation of food allergies. However, in practise, not all
patients will agree to perform the oral challenge. Both of our
patients refused oral provocation, since they remained without
further allergic reactions to egg proteins after diagnostics and
counselling.

Discussion

Egg allergies can usually be confirmed by the combination of
medical history, prick test, and specific IgE. Prick test with native
hen's egg is more sensitive that with commercial egg extracts
[4, 5]. It must be kept in mind that different assays for specific
IgE provide variable, not uniformous results considering the
absolute values. In case of follow-up to verify immune tolerance
development, the same assay should be used [6].

Egg allergens are often hidden allergens in food. An
investigation of snacks and pastries identified undeclared
egg allergens in 12% and 6% of cases [7]. That is a source of
discomfiture among consumers. Egg allergies rank on foremost
position for smaller children in the Germany Anaphylaxis
Registry [8].

Molecular allergy represents a milestone the diagnostic of
food allergies. For the first time, tailored risk profiles can be
assessed for individual patients. Patients can be counselled
accordingly to avoid the identified allergens or to prepare the
food - in case of thermolabile allergens - in a proper way. This
will reduce the risk of severe allergic reactions [9]. A limitation is,
however, that most clinical trials have been performed in small
children, not adults.

Case 1 demonstrates cross-reactivity of egg allergens among
different bird species. Hen (Gallus domesticus) and quail (Coturnix
coturnix) belong to the same family of Galliformes. The known
major allergens of hen's eggs are ovomucoid (Gal d 1), ovalbumin
(Gal d 2), ovotransferrin (Gal d 3), lysozyme (Gal d 4), and
albumin (Gal d 5). Proteins with the highest sensitizing potential
can be found rather in the white egg (Gal d 1-4) compared to egg
yolk (Gal d 5) [1-4].

Defined single molecules without contamination with sensitizing side chains

Not all relevant antigens are available yet

Standardisation

Production delicat

Identification of individual sensitization patterns

Polymorphism of natural allergen extracts is difficult to recreate

Differentiation between genuine sensitization and cross-reactivity

Interpretation needs experience

Higher specificity and sensitivity

Higher costs

In contrast, ovomucoid is thermo-stabile and resistant to
digestion. Ovalbumin is the dominant allergen component of
hen's eggs and represents 11% of hen's eggs protein amount [3,
4]. The protein can be identified in small amounts not only in
food but vaccines against yellow fever and influenca. This might
theoretically cause problems in highly sensitized patients. A
Japanese study investigated the risk of influenca vaccination in
children allergic to eggs but could not find any allergic reactions
to the vaccine [10].

Low-level specific IgE against ovomucoid may be a hint for
mild symptoms after consumption of boiled eggs as in case 2 or
of tolerance induction. A failure of tolerance development is often
associated with increased specific IgE againts ovomucoid [5].

There is a case report of a child without hen's egg allergy
who developed food-protein enterocolitis syndrome after
consumption of quail eggs. Such reaction is not IgE mediated. Due
to diarrhoea and vomiting allergic shock can be seen in up to 20
% of patients [11].

Patients with ovomucoid-allergy are not protected by food
processing. Strict avoidance of eggs or oral tolerance induction are
the alternatives. Recently, monoclonal IgE antibody omalizumab
has been used off-label in such cases [12].